Question is, on a pleasant, comfortable Saturday in the fall, why would you want to be playing or watching a football game indoors? An indoor stadium makes sense if you're playing football well into January or something like that.
And why would that be a recruiting benefit, necessarily? Do you really think a player is going to choose ISU over Iowa, Wisconsin, etc because of an indoor stadium? I don't think it's whether it's indoor or outdoor, but the fact that it's a new stadium. After that, it's going to be all about the atmosphere. Unless you get butts in the seats, and get them loud, it won't matter if you're inside or outside...an empty stadium is an empty stadium.